<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    //  obj.a = 100
    const obj = {}
    // boj.a = 100
    // console.log(obj.a);
    // obj.a = 200
    // console.log(obj.a);
    var val = 100
    Object.defineProperty(obj,'a',{
      get(){
        console.log('只要有人访问我是知道的');
        return val

      },
      set(newVal){
        console.log('只要有人修改我是知道的');
        val = newVal
      }
    })
    console.log(obj.a);
    obj.a = 200
    console.log(boj.a);

  </script>
</body>
</html>
